1. Field of the Invention
This invention relates to a material strength measuring apparatus, and more particularly to an apparatus for measuring material strength for various materials having a curved surface or an irregular surface through measuring rotational cutting resistance.
2. Description of the Prior Art
FIG. 10 is a front view of a conventional apparatus for measuring adhesive strength of a coated film which is disclosed in Japanese Laid Open Patent Application No. Showa 63-37237 titled "Apparatus for Measuring Adhesive Strength of Coated Film". In the figure, a specimen mounting base 34 is fixed onto a first sliding member 33 which is pivotally mounted on a guide shaft 32 immovably fastened to a supporting stand 31. A coated plate 35 to be a specimen is mounted onto the specimen mounting base 34 by means of a specimen fixing implement 36. A screw-threaded rod 38 is screw-engaged in a nut 37 coupled to the specimen mounting base 34 and an end of the screw-threaded rod 38 is connected to a motor 39. The first sliding member 33 can move linearly in the horizontal direction along the guide shaft 32. A second sliding member 42 slidable moves on and along a guide shaft 41 fixed on the supporting stand 31 through a first connecting member 40. A second connecting member 43 fixed on the second sliding member 42 is connected to a third connecting member 45 fixed on a third sliding member 44, whereby a guide shaft 46 causes the third sliding member 44 to slide up and down. An end of the guide shaft 46 constitutes a supporting body for a cutting blade 47, while the other end thereof forms a screw-threaded rod where a thumb nut 48 for holding the cutting blade and a weight 49 are disposed. The weight 49 functions to adjust and establish the press-contacting force of the cutting blade 47 to the film coated plate 35. A front end portion of a micrometer 50 fixed to the third connecting member 45 is urged to the second connection member 43 in such a manner as to cause the front end portion of the cutting blade 47 to be in parallel with surface of the test specimen material.
A pressure detector 51 fixed on the connecting member 40 detects a repulsive force to be generated against the cutting blade 47 through the second sliding member 42 and the connecting rod 52. Measured data are converted by means of an A/D converter 53, then the A/D converted data are introduced as inputs into a personal computer 45 wherein they are subjected to waveform-processing with use of a Fourier transformation program, power spectra, and a graph of a self-correlation function. A temperature regulator 55 such as a thermo-module is used for adjusting a temperature of the test specimen.
A coated plate having, for example, a length of 150 mm, a width of 70 mm, and a thickness of 1 mm was used as the test specimen 35 and a part of the coated film is peeled off in a size of 2 cm square to expose the surface of the base material. The partially exposed coated plate 35 is mounted on the specimen mounted base 34 by means of the specimen fixing implement 36 in such a manner that it may be tightly attached to the base, and then the cutting blade 47 having a blade width of 4 mm is applied onto the exposed portion of the coated plate 35 and pushed against the coated plate by means of the weight 49 so that a pressing force of 600 gf may be exerted to it. Then, adjustment is made by a micrometer 50 to bring the edge of the cutting blade 47 in parallel with the test specimen.
Then, a motor 39 is driven to shift the coated plate 35 at a velocity of 1 mm/min, while detecting by means of the pressure detector 51 an interfacial cutting resistance to the cutting blade 47 which has been transmitted to it through the connecting rod 52 fixed to the second sliding member 42. At first, a part of the base material is cut in 5 mm length, followed by cutting a part of the coated film in 15 mm length. Then, by use of the thermo-module 55, the temperature of the coated plate is regulated to a constant temperature level ranging from -10.degree. C. to 60.degree.C.
FIG. 11 is a characteristic diagram showing the cutting resistance to the cutting blade at the interface between the base material and the coated film, in which the ordinate axis denotes the cutting resistance (kg) at an interface between the coated layer and the base material, and the abscissa axis represents a cutting length (mm) of the interface between the coated film and the base material. As seen form the characteristic diagram, the measured data appear in the waveform, in which "A" indicates the cutting resistance of the surface of the base material, and "B" indicates the cutting resistance of the interface between the coated film and the base material.
FIGS. 12 to 14 are graphical representations corresponding to FIG. 11, respectively showing the cutting resistance at the interface in case the conditions for the surface treatment of the base material are varied for coating an epoxy type film by electrical deposition, in which FIG. 12 is the characteristic diagram of the interfacial cutting resistance of the test specimen which has been subjected to the surface preparation of the base material with use of zinc phosphate in acicular crystal; FIG. 13 is the characteristic diagram of the interfacial cutting resistance of the test specimen which has been subjected to the surface penetration of the base material with use of zinc phosphate in columnar crystal; and FIG. 14 is the characteristic diagram of the interfacial cutting resistance of the test specimen which has been subjected to the test specimen which has been subjected to the surface preparation of the base material with use of zinc phosphate in scaly crystal. It will be seen from these characteristic diagrams that, even when the coated film is of the same material, if the formation treatment of the treated steel plate differs, the adhesive strength of the coated film differs accordingly with the consequence that the interfacial cutting resistance and the waveform become varied as shown in FIGS. 12 to 14.
FIG. 15 is a flow chart for the wave form analysis program, in which the measured data 55 of the interfacial cutting resistance is processed by the A/D converter 56, input into the personal computer 57, and output to a program file 58. After producing the output data of the program file 58 in the form of a graph, a processing range is input by a cursor from the image plane, followed by processing 60 of the measured data by use of the subsequent Fourier conversion program 59 to output the result of the conversion into the film.
Then, the input is introduced into the respective files of Fourier spectra, power spectra and self-correlation function, from which graphs are output at 61.
FIG. 16 is a power spectral diagram to be obtained by the Fourier conversion of the interfacial cutting resistance of a urethane type coating material for each heating time of 0 hr., 100 hrs., 300 hrs., and 650 hrs.. In this graphical representation, the abscissa represents the number of vibration (cps) and the ordinate denotes power spectrum (cm.sup.2 /sec.sup.3). From this graph, it will be seen that, in the heat-resistance test at 160.degree. C., the power spectrum tends to lower while the peak number of vibration tends to increase as the heating time becomes prolonged.
The interfacial cutting resistance is a composition force of the adhesive strength of the coated film and the material strength, the breaking form of which is recorded as a waveform. By subjecting the measured values of the interfacial cutting resistance to the Fourier conversion and then carrying out the waveform analysis, there can be obtained information for clarifying the nature of the phenomenon.
By the way, in the above-described conventional device for measuring the adhesive strength of the coated film, explanation has been made as to an instance of using a general coated plate having a film thickness of a few tens of micrometers or above. It may, however, be feasible that film be coated on a plastic plate to obtain the same effect as in the above-mentioned conventional example.
With the above-described conventional apparatus for measuring adhesive strength of a coated film, it was necessary to provide the coated plate (35) for the film testing purpose and to analogize the adhesive strength of the coated film of the object to be tested on the basis of this result of measurement, hence there remained problems with respect to reliability and precision of the result of the measurement of analogy.
There was also a problem such that the shape of the specimen must be flat and specimens having curved surface or an irregular surface can not be tested since the specimen moves linearly during the test.